Double Sideband Suppressed Carrier Modulation Research Articles

High-accuracy optical vector network analyzer for optical notch and bandpass responses

A high-accuracy optical vector network analyzer (OVNA) based on optical carrier-suppressed double sideband (CS-DSB) modulation is proposed and experimentally demonstrated. The ±1st-order sideband signals are generated by CS-DSB modulation and then pass through the symmetric optical device under test (DUT). The band-stop or band-pass responses can be realized by detecting and processing the double frequency of the driven RF signal. Compared with the conventional symmetrical DSB-based OVNA, the measurement accuracy is improved by eliminating the errors caused by the even-order sidebands, and the complexity is reduced as the proposed method with only one step measurement can avoid the complex postprocessing. In addition, the optical carrier is aligned to the center frequency of the DUT by employing the Pound–Drever–Hall (PDH) technique, which provides stable measurement. At the same time, the limitation that the band-pass responses cannot be measured by the traditional single-sideband (SSB)-based OVNA is overcome. Additionally, accurate magnitude and phase responses of the DUT near the optical carrier can be also achieved since the proposed OVNA is optical filter-immune. The proposed method is theoretically analyzed and verified by experiment. A Fabry–Perot (FP) interferometer serves as the symmetric DUT; the band-stop responses in a frequency range of 6 GHz are obtained with a resolution of 1.2 MHz; and the band-pass responses with the range from 0 to 13 GHz offsetting the optical carrier are also obtained. The measurement time can reach up to 30 min with high stability. The proposed OVNA offers enhanced accuracy and a stable approach for applications in photonic systems and other innovations.

Optimization and control of cold atom interference phase shift based on laser double-sideband suppression

Using the electro-optical modulation method to generate Raman beams for cold atom interference is one of the better methods for constructing a more compact and robust laser system. But this way will generate some residual sidebands resulting in the additional interference phase shift, which can affect the measurement accuracy of cold atom interferometer. In order to weaken the effect of laser modulation sidebands on the phase shift of cold atom interference, a double-sideband suppressed-carrier modulation laser system for cold atom interference is constructed. Based on the designed laser system, the principle of double-sideband generation and suppression is analyzed in detail, and some residual sidebands are adjusted and controlled. Moreover, some important optical parameters that affect the phase shift of cold atomic interference, such as the initial distance between the Raman retro-reflection mirror and the atomic cloud, the interrogation time between two adjacent Raman pulses, the laser modulation depth and the initial velocity of the atomic cloud, are discussed and optimized. By optimizing these relevant parameters, the influence of residual modulation sidebands on the phase shift of cold atomic interference is weakened drastically. The research results indicate, making use of the method of double-sideband suppression, the phase shift of cold atomic interference can be optimized to 0.7 mrad when the initial distance between the Raman retro-reflection mirror and the atomic cloud is 105 mm, and the interrogation time between two adjacent Raman pulses is 82 ms. More importantly, this work can provide a method for weakening the influence of Raman sideband effect on the phase shift of cold atom interferometer, and the corresponding laser system can be applied to other inertial sensors such as atomic gravimeter or atomic gravity gradiometer.

Amplitude and time-dependence of ultrasonic radiation force on modulation frequency computed from specular reflection contributions

Ever since the late 1970s, there has been interest in the modulated radiation pressure of double sideband suppressed carrier (DSSC) ultrasound, because the associated radiation pressure oscillates at a single low frequency. Recent research considers situations, where the radius of curvature of the illuminated objects greatly exceeds the wavelength at the implicit carrier frequency of the ultrasonic illumination [Marston et al., J. Acoust. Soc. Am. 149, 3042–3051 (2021); 150, 25–28 (2021)]. Furthermore, the objects of interest, cylinders, and spheres in water are taken to be sufficiently highly reflecting that the radiation force can be shown to be dominated by contributions associated with specular reflection. In such cases, it is helpful to geometrically analyze the amplitude and time dependence of the oscillatory radiation force for perfectly reflecting objects, where the relevant integrals of the stress projections can be carried out analytically. The results are expressed using Bessel and Struve functions. They explain how the amplitude and phase of the force depends on the DSSC modulation frequency in agreement with partial-wave-series based calculations. The approach is relevant in other situations. [Work supported by the U. S. Office of Naval Research.]

Distributed strain and temperature fast measurement in Brillouin optical time-domain reflectometry based on double-sideband modulation.

A novel distributed strain and temperature fast measurement method in Brillouin optical time-domain reflectometry (BOTDR) system based on double-sideband (DSB) modulation is proposed. The single-wavelength probe light is modulated into dual-wavelength probe light with a fixed phase difference by using carrier suppressed DSB modulation. The interaction between the Brillouin scattering signals corresponding to dual-wavelength probe light forms a Brillouin beat spectrum (BBS). The distributed temperature and strain are obtained by only measuring the peak power trace of the BBS and one of the slope power trace of the two Brillouin gain spectrum (BGS) corresponding to dual-wavelength probe light. The proposed method does not require scanning the Brillouin spectrum and does not require using optical fibers with multiple Brillouin scattering peaks as sensing fibers, and thus features fast measurement speed and wide variety of sensing fiber types. In a proof-of-concept experiment, the temperature uncertainty of 1.3 °C and the strain uncertainty of 36.3 με are respectively achieved over a 4.5-km G.657 fiber with 3 m spatial resolution and 30 s measurement time. The experimental measurement uncertainties of temperature and strain of the proposed method are almost equivalent to that of the method by using BGS scanning and special fibers.

Dual-Wavelength Light Source Assisted Frequency Response Measurement Method of Photodetectors

Dual-wavelength light source assisted frequency response measurement of photodetectors based on double-sideband suppressed-carrier modulation is proposed in this letter. In this method, a directly modulated laser with a modulation frequency of f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> combined with an optical tunable filter is used to generate a dual-wavelength carrier, which can be highly stable since only one light source is introduced. The dual-wavelength carrier generates two pairs of first-order sidebands under double-sideband suppressed-carrier modulation of the Mach-Zehnder modulator at frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> . Afterwards, the modulated signal is injected into the photodetector under test, and the frequency response of the photodetector can be extracted by recording the electric power at specific frequencies. Based on this method, we used a 35-GHz modulator to measure the frequency response of photodetectors with bandwidth of 15 GHz and 43.5 GHz respectively. Moreover, a comparison of the results is performed between our method, the swept frequency method, and electro-absorption modulator deduction method. The results show that the new method extends the frequency response measurement range from f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> to f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> +2f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> , and the influence of the modulator on the frequency response measurement results is reduced simultaneously.

Chip-based microwave photonic frequency mixer (Invited)

A microwave photonic frequency mixer constituted of an optically-carried local oscillator (LO) and a wavelength-division modulator was proposed. The wavelength-division modulator chip, which was consisted of a silicon phase modulator, two micro-ring filters, a photodetector, two optical couplers, and two grating couplers, was designed and fabricated. Based on the chip, a microwave photonic harmonic frequency mixer was implemented. In the experiment, an optically-carried LO was generated by double-sideband suppressed-carrier modulation at a Mach-Zehnder modulator. An RF signal from 6 to 16 GHz was successfully converted into a signal with a frequency of 33 to 23 GHz. In order to suppress the remaining mixing spurs, two solutions, i.e., increasing the rejection ratio of the micro-ring filter to decrease the intensity of the leaked optically-carried LO and introducing an optical phase shifter to correct the phase of the leaked optically-carried LO, were proposed and verified by simulation. It should be noted that the latter is simpler and more suitable for photonic integration.

Design of a Multipurpose Photonic Chip Architecture for THz Dual-Comb Spectrometers.

In this work, we present a multipurpose photonic integrated circuit capable of generating multiheterodyne complex Dual-Combs (DC) THz signals. Our work focuses on translating the functionality of an electro-optic tunable DC system into a photonic chip employing standard building blocks to ensure the scalability and cost efficiency of the integrated device. The architecture we analyze for integration is based on three stages: a seed comb, a mode selection stage and a DC stage. This final DC stage includes a frequency shifter, a key element to improve the final detection of the THz signals and obtain real-time operation. This investigation covers three key aspects: (1) a solution for comb line selection on GHz spaced combs using OIL or OPLL on photonic chips is studied and evaluated, (2) a simple and versatile scheme to produce a frequency shift using the double sideband suppressed carrier modulation technique and an asymmetric Mach Zehnder Interferometer to filter one of the sidebands is proposed, and (3) a multipurpose architecture that can offer a versatile effective device, moving from application-specific PICs to general-purpose PICs. Using the building blocks (BBs) available from an InP-based foundry, we obtained simulations that offer a high-quality Dual-Comb frequency shifted signal with a side mode suppression ratio around 21 dB, and 41 dB after photodetection with an intermediate frequency of 1 MHz. We tested our system to generate a Dual-Comb with 10 kHz of frequency spacing and an OOK modulation with 5 Gbps which can be down-converted to the THz range by a square law detector. It is also important to note that the presented architecture is multipurpose and can also be applied to THz communications. This design is a step to enable a commercial THz photonic chip for multiple applications such as THz spectroscopy, THz multispectral imaging and THz telecommunications and offers the possibility of being fabricated in a multi-project wafer.

Comment on oscillatory optical and acoustical radiation pressure

This comment is timely because of a paper [JQSRT 250 (2020) 106994] on the time dependence of optical radiation forces resulting from modulated illumination. While the acoustic analog of oscillatory radiation pressure was mentioned, the omission of early developments contributes to the introduction of terminology that is not sufficiently descriptive. For example, the illumination considered was double-sideband suppressed carrier modulation (DSB-SCM), as distinct from conventional “amplitude modulation” (AM), contrary to the impression given. Properties of DSB-SCM and AM radiation pressure are reviewed along with some early acoustical and optical modulated radiation pressure experiments, selected recent research, and some analytical and related concerns.

High-power spectral beamsplitter for closely spaced frequencies.

An experimental realization of a compact, high-power spectral beamsplitter for nearly equal frequencies and identical polarization based on two-beam interference in a free-space Mach-Zehnder interferometer is presented. We demonstrate the power- and cost-efficient generation and subsequent spatial separation of two laser tones from a single sum-frequency-generation stage using double-sideband suppressed-carrier modulation in the infrared, and beam splitting in the visible at high power. The interferometer spectrally splits >98 % of the incident power when accounting for bulk absorption. The beamsplitter can be constructed identically for any power or spectral range required for which suitable optics are available.

Ultra wideband measurement for arbitrary spectral response using double sideband modulation and low-frequency detection

An ultra-wideband measurement for arbitrary optical magnitude response is proposed and experimentally demonstrated by using optical carrier-suppressed double sideband modulation and fixed low-frequency detection. Compared with previous optical single sideband modulation-based methods, the proposed scheme doubles the measurement range. Moreover, the response can be detected at a fixed low frequency by incorporating microwave photonic frequency down-conversion. The proposed approach has the merit of measuring arbitrary response avoiding high-speed and wideband detectors. To verify the concept, simulation and experiment are carried out. The magnitude responses of two fiber Bragg gratings, which have bandwidths of 19.8 GHz and 67 GHz, are characterized with a resolution of 10 MHz by using a 43.5 GHz microwave signal source.

Anti-chromatic dispersion transmission of frequency and bandwidth-doubling dual-chirp microwave waveform.

A photonic approach to realizing anti-chromatic dispersion transmission for a frequency and bandwidth-doubling dual-chirp microwave waveform is proposed and experimentally demonstrated. The system has no requirement on polarization devices or optical filters for only the integrated dual-drive dual-parallel Mach-Zehnder modulator employed. To overcome chromatic dispersion, the carrier frequency suppression approach is proposed. The anti-chromatic dispersion process is accomplished in a central station and independent to carrier frequency, fiber length, and dispersion coefficients. An experiment is conducted to verify the analysis. Dual-chirp waveforms at 13GHz with a bandwidth of 0.8GHz and time duration of 1μs are obtained. After 25km fiber transmission, the proposed approach shows a relatively flat curve in a frequency-power diagram, while the normally carrier-suppressed double-sideband modulation method experiences a significant power fading for fiber dispersion.

A Wideband Photonic RF Receiver With Lower IF Frequency Enabled by Kramers–Kronig Detection

Featuring the benefits of wideband operation, flexible tunability, and enhanced electromagnetic immunity, photonic down-conversion is a promising technique for future RF heterodyne receiver. However, due to the square-law detection of the photodiode (PD), the down-converted signal suffers from signal-signal beat interference (SSBI). In this paper, we demonstrate a photonics-based RF heterodyne receiver using direct detection and Kramers–Kronig (KK) algorithm. The RF signal and the LO signal are modulated on an optical carrier using carrier-suppressed double-sideband (CS-DSB) modulation. A single-ended PD is severed as the mixing element to produce the intermediate frequency (IF) signal. Thanks to the SSBI mitigating ability provided by KK processing, the need of a frequency gap between the RF signal and the LO signal can be obviated, resulting in a lower IF. This allows a low-speed PD and an analog-to-digital converter with a lower sampling rate to be employed. The performance of the RF receiver is verified via reception of an RF vector signal with 16-quadrature amplitude modulation (QAM). With no frequency gap between the RF signal and the LO signal, the experimental results show that error vector magnitude (EVM) of the down-converted 16-QAM signal is 4.31%, while the EVM is 13.1% without KK processing. To the best of our knowledge, this is the first time KK processing is applied for direct detection of optical CS-DSB signals. Without long-haul fiber transmission, CS-DSB modulation is preferable for photonic RF frequency conversion due to its easy implementation.

Accurate optical vector network analyzer based on optical double-sideband suppressed carrier modulation

A high-accuracy optical vector network analysis (OVNA) based on optical suppressed carrier double-sideband (DSB) modulation and the Pound Drever Hall (PDH) technique is proposed and demonstrated. The accurate and stable frequency responses can be achieved by transmitting the optical carrier suppressed DSB modulation signals through the DUT, and then detecting the reflected signals. Compared with the traditional DSB-based OVNA, the measurement accuracy is improved by eliminating the errors caused by the even-order sidebands. Furthermore, the stability of the OVNA system can be kept by using the PDH feedback loop. An experiment is accomplished. The frequency responses of the FP interferometer are achieved with little measurement error induced by high-order sidebands, and no repeated frequency response appears even when the test time reaches up to 30 min. This novel method is simple and accurate, and would be used for charactering the symmetric ultra-high Q optical devices.

Tunable dual-passband microwave photonic filter with a fixed frequency interval using phase-to-intensity modulation conversion by stimulated Brillouin scattering.

An approach to realizing a highly selective and stable tunable dual-passband microwave photonic filter (MPF) is proposed and experimentally demonstrated, in which two passbands have a fixed frequency interval. The MPF is achieved based on phase-to-intensity modulation (PM-IM) conversion by stimulated Brillouin scattering (SBS). The kernel of the proposed scheme is generating a two-tone pump by first frequency-downshifting the optical carrier through self-induced SBS in a spool of single-mode fiber (SMF), and then modulating it in carrier-suppressed double-sideband modulation mode. Making use of Brillouin frequency shift difference between the SMF and the high nonlinear fiber used for PM-IM conversion, two passbands with a fixed frequency interval equal to 2 times the Brillouin frequency shift difference between the two fibers can be achieved. Through simply varying the modulation frequency, the two passbands can be synchronously shifted back and forth. In the experiment, a tunable dual-passband MPF with a fixed frequency interval of 2.434GHz is demonstrated in the frequency range of 0-9.644GHz, where the out-of-band rejection ratio and the 3-dB bandwidth of the passbands are measured to be larger than 20dB and smaller than 57MHz, respectively.

Freely Tunable Dual-Passband Microwave Photonic Filter Based on Phase-to-Intensity Modulation Conversion by Stimulated Brillouin Scattering

An approach to achieving a highly selective and stable microwave photonic filter (MPF) with two passbands independently tunable is presented. The dual-passband MPF is realized based on phase-to-intensity modulation conversion by stimulated Brillouin scattering. In the proposed scheme, a freely tunable two-tone pump is generated by passing the optical carrier through two cascaded dual-parallel Mach-Zehnder modulators (DPMZMs), with one acting as a frequency shifter with assistance of an electrical 90° hybrid and the other one working at carrier-suppressed double-sideband modulation mode to generate two-tone pump. The two passband locations of the MPF can be freely set by adjusting the frequencies of the two single-tone signals applied to the two DPMZMs. In the experiment, a dual-passband MPF with flexible passband tunability and shape-invariant tuning is demonstrated in the frequency range of 0-9.644 GHz, where the out-of-band rejection ratio and the 3-dB bandwidth of the passbands are measured to be larger than 25 dB and smaller than 55 MHz, respectively. The proposed MPF scheme also has the ability to tailor the shape and the width of the two passbands, which is a promising solution to achieve a freely programable dual-passband MPF.

Photonic down‐conversion and linearisation with tunable IF bandwidth and improved spurious‐free dynamic range

A scheme for simultaneous down-conversion and linearisation of radio-frequency (RF) signals is proposed and demonstrated. Based on carrier-suppressed double-sideband modulation, the input RF signal can be down-converted to any intermediate frequency (IF) tone in the range of 8–12 GHz. Compared with the down-conversion scheme with two cascaded intensity modulators, the proposed scheme has improvement of >21 dB of the suppression ratio of third-order intermodulation distortion and 6.17 dB of spurious-free dynamic range.

Transparent intersatellite optical wireless communication link with double sideband-suppressed carrier modulation and coherent homodyne detection

In this paper, we present an intersatellite optical wireless communication (IsOWC) link with double sideband-suppressed carrier (DSB-SC) modulation and coherent homodyne detection (CD), which enables transparent transport of multiband radio frequency (RF) signals. The performance of transparent multiband IsOWC link employing DSB-SC/CD and phase modulation with CD (PM/CD) is investigated. The theoretical model considers the finite extinction ratio (ER) of a Mach-Zehnder modulator (MZM) and the saturation property of an optical booster amplifier. The expressions of RF gain, noise figure (NF) and third-order spurious-free dynamic range (SFDR) are derived considering the third-order intermodulation product and amplifier spontaneous emission noise for both architectures. Numerical results for RF gain, NF, and third-order SFDR are given for demonstration. Results indicate that DSB-SC/CD can provide higher linearity and better sensitivity than PM/CD. The performance of the DSB-SC/CD scheme is obviously influenced by the ER of MZM. The gain of the optical preamplifier and the power of a local oscillator optical signal should be optimized to obtain satisfactory performance.

Millimeter-Wave Radio-Over-Fiber Network for Linear Cell Systems

We discuss and propose millimeter-wave linear cell systems for signal distribution on railway radiocommunication systems between train and trackside, and a foreign object debris detection system for airport runways using the radio-over-fiber network technology. Linear cell configurations based on wavelength-division multiplexing (WDM) and power-splitter-based distribution networks are discussed and demonstrated experimentally. A single-sideband modulation for data transmission in an intermediate frequency over a fiber system is successfully transmitted with an ultrafast wavelength-tunable laser diode for WDM routing to track the train car within 3 $\mu$ s. Radar signal distribution by an optical double-sideband suppressed-carrier modulation mitigates the dispersion effect of the fiber cable to transmit a 32-GHz signal into the remote radar heads.

All-Optical Microwave Photonic Downconverter With Tunable Phase Shift

An all-optical microwave photonic frequency downconverter with tunable full range continuous phase shift is presented. In the proposed system, the radio frequency (RF) and local oscillator (LO) signals modulate two sub Mach–Zehnder modulators (MZMs) in an integrated dual-parallel MZM (DPMZM), respectively. The two sub-MZMs are both biased at the minimum transmission point to implement the carrier-suppressed double-sideband modulation. An optical bandpass filter is then used to retain the +1st order RF and LO sidebands. When the two sidebands are send to a photodetector, an intermediate frequency (IF) signal is produced, and the phase of the converted IF signal is linearly changed by adjusting the bias voltage of the parent MZM in the DPMZM. An experiment is carried out. An RF signal can be downconverted to a phase-tunable IF signal, and the measured spurious-free dynamic range reaches 100.2 dB·Hz2/3. The phase deviation and power ripple of the IF signal are less than 2° and 0.26 dB, respectively. The all-optical design makes the system bandwidth unlimited by electrical components. Meanwhile, since the proposed microwave photonic link can simultaneously implement frequency downconversion and full range phase shift of the converted IF signal, it provides a compact alternative for the applications including radio-over-fiber system and phased-array beamforming.

Precise Optical Modulation Using Extinction-Ratio and Chirp Tunable Single-Drive Mach–Zehnder Modulator

We analyzed the complex transfer function and modulation spectrum of the Mach–Zehnder (MZ) modulator with optical power and phase change imbalances. From the calculations, we found that the characteristic operation can be obtained in three cases: high extinction ratio, zero-chirp, and straight-line trajectory in the IQ plane. However, the results also indicate that we cannot achieve an operation equivalent to that of the ideal modulator, due to the small parasitic chirp in a single-drive modulator. To control the extinction ratio and chirp parameter individually, we propose an integrated modulator with some tunable Y-branches. By using the optical-power-imbalance tunable modulators, we experimentally demonstrate the characteristic operations and obtain the modulation spectrum equivalent to the ideal MZ modulator. However, compared to the ideal amplitude modulator, MZ modulators exhibit an intrinsic nonlinearity in the sinusoidal response. Therefore, we used a third-order nonlinearity compensation method using the superposition of electrical third-order harmonics. The measured spectrum consisted of only first-order modulation sidebands, which is equivalent to the ideal double-sideband suppressed-carrier modulation.